There has been known to provide a plurality of wheel speed sensors in a vehicle, such as an automobile, in order to detect rotational speeds of a plurality of wheels of the vehicle. Further, Japanese kohyo (PCT) Patent Publication No. 2005-515923 discloses an air pressure generation unit provided for each wheel and including an air pump driven through rotation of the wheel so as to generate compressed air to be supplied to a tire air chamber of the wheel and being capable of maintaining a tire pressure of the wheel between a lower limit set value and an upper limit set value. Moreover, Japanese Patent Application Laid-Open (kokai) No. H7-137515 discloses a plurality of pressure sensors respectively detecting the tire pressures of a plurality of wheels.
Therefore, in a tire-pressure control apparatus provided in a vehicle such as an automobile, it is possible to provide the above-described air pressure generation unit for each of a plurality of wheels so as to maintain the tire pressure of the wheel between a lower limit set value and an upper limit set value, and to detect and monitor the tire pressure of each wheel by use of a pressure sensor. However, the conventional techniques cannot determine whether each air pressure generation unit is normal or anomalous and whether each wheel speed sensor and each pressure sensor are normal or anomalous. Therefore, there is room for improvement of the reliability of the tire-pressure control apparatus.